This invention relates generally to a method for making retreaded tires and particularly to a method for making retreaded tires that eliminates the need for spray cement normally applied to the tire casing.
Retreaded tires have been available for many years and provide an economical way to gain additional use out of a tire casing after the original tread has become worn. According to one conventional method of retreading, sometimes referred to as cold process retreading, the remaining tread on the used tire is removed by a special buffing machine that grinds away the old tread and leaves a buffed surface to which a new layer of tread may be bonded.
Removal of the old tread from the tire casing provides a generally smooth treadless surface about the circumference of the tire casing. The tire casing may then be examined for injuries, often called skives, which are filled with a repair gum. After completion of the skiving process, the buffed surface is sprayed with a tire cement that provides a tacky surface for application of bonding material and new tread. Then a layer of cushion gum is applied to the back, i.e., the inside surface, of a new layer of tread. The cushion gum and tread are applied in combination about the circumference of the tire casing to create a retreaded tire assembly ready for curing. The cushion gum forms the bonds between the tread and the tire casing during curing.
Following assembly of the tire casing, cement, cushion gum and tread, the overall retreaded tire assembly is placed within a flexible rubber envelope. An airtight seal is created between the envelope and the bead of the tire. The entire enveloped tire assembly is placed within a curing chamber, and subjected to pressure and a raised temperature for a specific period of time. The combination of pressure, temperature and time chemically bonds the layer of cushion gum to both the tire casing and the new tire tread.
The above-described method of cold process retreading works well and provides high quality, retreaded tires. However, in certain applications it would be advantageous to eliminate the spray cement. This is particularly true in geographical areas where there is increased regulation of the use of chemicals within spray cement. Generally, available spray cements include either heptane solvent or methyl chloroform. The heptane solvent has been found to contribute to smog formation, and methyl chloroform, although it does not cause smog, has tended to be substantially more expensive then heptane solvent.
Use of spray cement can also add to the cost of producing retreaded tires due to the product cost and equipment cost. For example, because cementing of the tire casing should only be dome in a well ventilated spray booth, retreading shops must purchase appropriate ventilation equipment. Elimination of the spray cement thus eliminates the need to purchase ventilated spray booths.
A potential solution to smog problems associated with using heptane solvent is the installation of solvent capture equipment at each retreading shop. However, this solution is disadvantageous due to the cost of the equipment and the operational and maintenance costs. The present invention addresses the drawbacks associated with using spray cement during retreading of tires.
The present invention includes a method for retreading a tire that comprises the steps of removing the tire tread from a tire casing to present a buffed surface. Then, a layer of cushion gum is applied directly to the buffed surface without spraying cement over the buffed surface. A tread layer is wrapped about the layer of cushion gum, and finally, the tire is treated to form bonds between the casing and the layer of cushion gum and between the tread layer and the layer of cushion gum.
Another unique aspect of the invention is a retreaded tire assembly prepared for insertion into a pressurized heating chamber. The tire assembly includes a tire casing having a pair of side walls and a radially outer wall spanning the pair of side walls. The radially outer wall has a buffed surface disposed about the outer circumference of the tire casing. A layer of cushion gum is disposed directly against the buffed surface, and a tread layer is disposed against the cushion gum about the outside circumference of the cushion gum. After appropriate heat and pressure treatment, the tire casing, cushion gum and tread layer became bonded into an integral retreaded tire that may be used on an appropriate over-the-road vehicle.